This is one of the most common nutrient deficiencies found in all cannabis plants, it will start initially in the lower leaves and cause them to turn a pale green color. Following this the leaves will turn yellow and start to die as the new growth in the plant siphons off the remaining nitrogen. The nitrogen deficiency will progress steadily up the plant and only the very top of the plant where the new growth is present will it be a vivid green color, the rest of the plant will be wilted and yellow as a result of the nitrogen deficiency.
A lack of nitrogen can be so damaging because it is one of the most important nutrients that your plant needs to function. It is responsible for producing the bulk of all chlorophyll and amino acids within your plant, while also being a key part of the photosynthesis process. A high percentage of plant tissue is also composed of nitrogen meaning a deficiency would severely restrict growth within the plant.
While this article is focusing on a lack of nitrogen, you should be aware that an excess of nitrogen is not good for your plant either. It will produce a more plump greener plant, however it will be more vulnerable to diseases and pests. Furthermore the stalks will lose flexibility and begin to turn brittle.
Any high quality soil or cannabis friendly nutrients should provide you with all the nitrogen you need so if you are using both of these and still experiencing yellowing leaves then you should start looking into other deficiencies because it may not be a nitrogen one. If you have not been using any additional nutrients or high quality soil then you should acquire a nitrogen booster so that you can enrich your plants feed to the required level.
It is also normal to see a small amount of yellowing leaves on a large cannabis plant so do not be too hasty to diagnose your plant with a nitrogen deficiency as that could result in you giving it too much nitrogen.
As soon as you enter the flowering stage you can worry less about your plants nitrogen levels. A nitrogen deficiency is actually ideal during this stage as high levels of nitrogen can prevent proper budding and also reduce the smell and taste of your final product. Most flowering nutrients will be low in nitrogen and I encourage you to use one of these to avoid this problem.